1,1-Dichloro-1-fluoroethane (HCFC-141b) and dichloropentafluoropropane (HCFC-225) are hydrofluorocarbons that are currently used as solvents, cleaning agents or the like but are subjected to regulation in view of the fact that each of 1,1-dichloro-1-fluoroethane and dichloropentafluoropropane causes a large effect on the global environment because of high ozone depletion potential (ODP). In the field of use of these hydrofluorocarbons, there has been a demand for alternative materials that do not exert an effect or exert a very small effect on the global environment.
On the other hand, 1-chloro-3,3,3-trifluoropropene is a fluorine-containing unsaturated hydrocarbon that has a double bond in its molecule and shows very low ODP and global warming potential (GWP). Attention is being thus given to the 1-chloro-3,3,3-trifluoropropene as one alternative material. Patent Document 1 discloses, as a first step for the production of 1,1,1,3,3-pentafluoropropane, a process of producing 1-chloro-3,3,3-trifluoropropene by reaction of 1,1,1,3,3-pentachloropropane with hydrogen fluoride in a gas phase. Patent Document 2 discloses a process of producing 1,1,1-trifluoro-3-chloro-2-propene (1-chloro-3,3,3-trifluoropropene) by reaction of 1,1,1,3,3-pentachloropropane with hydrogen fluoride in the absence of a catalyst as a first step for the production of 1,1,1,3,3-pentafluoropropane. Further, Patent Document 3 discloses a process of producing 1-chloro-3,3,3-trifluoropropene by reacting 1,1,1,3,3-pentachloropropane in a liquid phase at a temperature lower than 150° C. in the presence of either a Lewis acid catalyst or a mixture thereof in a reaction vessel, continuously extracting hydrogen chloride and 1-chloro-3,3,3-trifluoropropene generated in the reaction vessel and isolating 1-chloro-3,3,3-trifluoropropene
The above processes however have a problem that the selectivity of the target product becomes deteriorated due to the occurrence of many by-products.
In general, distillation is adopted in industrial production process to separate a liquid or a liquefiable gas mixture. In the case where, at the time of separation of the target product containing any by-product as impurity, the boiling point of the target compound is very close to the boiling point of the by-product compound, it is very difficult to efficiently separate the target compound from the impurity by distillation.
Extractive distillation is thus adopted as one effective distillation method. Herein, “extractive distillation” refers to a method of separating a mixture of at least two kinds of components after adding a third component of high boiling point as an extractant to the mixture and thereby changing the relative volatility of the components to be separated. For example, Patent Document 4 discloses that pentafluoroethane and chloropentafluoroethane can be separated favorably by extractive distillation with the use of 1,2-dichlorotetrafluoroethane as an extractant. Patent Document 5 discloses a process of separating pentafluoroethane and chloropentafluoroethane by extractive distillation with the use of a ketone such as acetone or n-pentane or a paraffin as an extractant. Further, Patent Document 6 discloses a process of separating pentafluoroethane and 1,1,1-trifluoroethane by extractive distillation with the use of a C1-C2 chlorocarbon or chlorohydrocarbon as an extractant.
As a technique relevant to the present invention, Patent Document 7 discloses a process of separating 1,1,1,3,3-pentafluoropropane from a mixture thereof with 1-chloro-3,3,3-trifluoro-trans-1-propene by distillation, wherein the distillation is performed in the coexistence of, as a third component, a saturated hydrocarbon compound having a higher boiling point than 1-chloro-3,3,3-trifluoro-trans-1-propene.